The long-term objective of our laboratory is to understand how the innate immune system recognizes and responds to pathogen invasion at the molecular level, especially since such defenses may be controlled by genomic elements. In particular, this study will focus on NK cell- mediated viral immunity to murine cytomegalovirus (MCMV) as it is controlled by the NKO linked Cmy1 locus. Notably NK cells are important contributors of host innate immune defenses to a range of pathogens including, viruses, bacteria, and protozoan parasites, through cytokines released (e.g. IFN-gamma) and direct cell-mediated cytotoxicity mechanisms. Moreover, NK cells directly limit viral replication in mice during murine cytomegalovirus (MCMV) infection, this capacity directly correlates with host survival during MCMV challenge, and NK cell-mediated immunity is directly regulated by the Cmv1 locus. Cmv1 was recently mapped within the distal NKC, however Cmv1 candidate sequences were not reported. In preliminary data, we report that an additional NKC encoded NK receptor (Ly- 49H) may be involved in MCMV resistance, but this NKC gene is physically and genetically separate from the CMv1 locus. Hence, we will determine whether more than one NKC locus is required MCMV resistance by assessing MCMV resistance in novel intra-NKC recombinant mice and Cmv1 minus/minus mice (Specific Aim 1). Novel Cmv1 coding sequences will be selected form C57BL/6 mice and from MCMV susceptible strains of mice. These sequences will be compared structurally and biochemically to identify a best Cmv1 candidate sequence. Confirmation of Cmv1 candidate sequences will be performed using a transgenic approach (Specific Aim 2). Finally, should genetic data be obtained implicating Ly49h in MCMV resistance immunity using a transgenic approach. Furthermore, this gene will be thoroughly characterized in C57BL/6 and several MCMV susceptible mouse strains (Specific Aim 3). Thus, these studies should clarify our understanding of NK cell recognition of viral infection and Cmv1-regulated immunity, as these are not currently understood mechanistically.